Conventionally, a user may use a meter or ask a technician to check malfunctioned power cables in a computer for removing the problem. For the former case, a meter is required. For the latter case, the charge of consulting a technician for help is not cheap. Further, an experienced technician may not come to help immediately when the computer problem occurs. Thus, the need for providing a simple, cheap device for detecting a malfunctioned power cable at its connector in a computer without using a meter exists.